1. Field of the Invention
The present invention relates to a distributing valve device for a heat accumulation type combustion system wherein exhaust gas containing a smelly substance, such as an organic solvent, is combusted and the organic solvent and other smelly substances are removed from the exhaust gas before the gas is discharged.
2. Description of the Prior Art
Conventionally, exhaust gas to be treated containing smelly substance (hereinafter referred to as merely "exhaust gas"), such as organic solvent etc., which is produced in a coat drying oven or the like, is treated in a heat accumulation type combustion system, and then the so treated gas is discharged outward.
Above mentioned heat accumulation type combustion system is well known through Japanese Patent Laid-Open Publication No. 7-305824(1995) and other relevant Publications. As schematically shown in FIGS. 7A to 10, the heat accumulation type combustion system includes a housing 1, a distributing valve device 10, and a feed/discharge device 15. The distributing valve device 10 consists of a stationary valve 11 and a rotary valve 12.
Within the housing 1, as shown in FIG. 7B, a plurality of passages 3 (3a.sub.1, 3a.sub.2, 3a.sub.3, 3b, 3c.sub.1, 3c.sub.2, 3c.sub.3, 3d) defined by radially extending partition walls 2 provided at predetermined interval in a circumferential direction of the housing 1 are formed. In each passage 3, known heat accumulators 4, each comprised of ceramic particles or the like, are arranged and connected to a communicating space provided above the passage 3. In the communicating space, a combustion device 5 is disposed, which includes, for example, a heater and a burner, which constitute a combustion chamber 6.
The stationary valve 11, as shown in FIG. 8, is comprised of a plate-form member disposed at a bottom opening of the housing 1 and has openings 16 (16a.sub.1, 16a.sub.2, 16a.sub.3, 16b, 16c.sub.1, 16c.sub.2, 16c.sub.3, 16d) corresponding to respective passages 3a.sub.1, 3a.sub.2, 3a.sub.3, 3b, 3c.sub.1, 3c.sub.2, 3c.sub.3, 3d.
The rotary valve 12, as shown in FIG. 9, is comprised of a plate-form member adapted to be rotated by a rotary shaft 12a, and has an opening 13a opposed to openings 16 of the stationary valve 11, for example, 16a.sub.1, 16a.sub.2, 16a.sub.3, and an opening 13c opposed to openings 16c.sub.1, 16c.sub.2, 16c.sub.3, and a purge gas supply opening 13b formed between openings 13a and 13c and upstream of the opening 13a in the direction of rotation of the rotary valve 12. In addition, a closed portion 13d is provided between the openings 13a and 13c and downstream of the opening 13a in the direction of the rotation of the rotary valve 12, where no opening is provided. For example, the opening 13a is used for supplying exhaust gas, and the opening 13c is used for discharging treated gas. Boundary portions of the openings 13a, 13b, 13c and of the closed portion 13d, and the outer periphery and inner periphery of the rotary valve 12 are fitted with a seal member 14 for preventing leakage of the exhaust gas and the treated gas from the clearance between the stationary valve 11 and the rotary valve 12 toward other opening.
According to the above described arrangement, the exhaust gas is supplied from a feeding port of a feed/discharge device 15 into the passages 3a.sub.1, 3a.sub.2, 3a.sub.3 through the opening 13a of the rotary valve 12 and the openings 16a.sub.1, 16a.sub.2, 16a.sub.3 of the stationary valve 11. The exhaust gas is guided from these passages into the combustion chamber 6, in which any organic solvent contained in the exhaust gas is combusted by the combustion device 5 such that the exhaust gas is heated to a temperature of 800 to 900.degree. C. Subsequently, the exhaust gas is allowed to flow into the passages 3c.sub.1, 3c.sub.2, 3c.sub.3, and during the process of passing through the passages, the exhaust gas heats up the heat accumulators 4 within the passages and then, the exhaust gas itself becomes treated gas by being cooled. The treated gas is discharged from a discharge vent of the feed/discharge device 15 to a predetermined site through the openings 16c.sub.1, 16c.sub.2, 16c.sub.3 of the stationary valve 11 and the opening 13c of the rotary valve 12.
Furthermore, the rotary valve 12 is rotated intermittently or continuously in the direction shown by an arrow in FIG. 9, such that supply and discharge of the exhaust gas and the treated gas are carried out by sequentially changing the openings and passages through which the exhaust gas and the treated gas are respectively allowed to pass. In this way, the exhaust gas passes through the heat accumulators 4 which have been already heated by passage of hot treated-gas therethrough, whereby the exhaust gas is preheated and then, it is conducted into the combustion chamber 6.
In the rotary valve 12, the purge gas supply opening 13b and the closed portion 13d are disposed in opposed relation between the exhaust gas supply opening 13a and the treated gas discharge opening 13c, each opening being partitioned by the seal member 14. As shown in FIG. 8, each sector-shaped opening 16 of the stationary valve 11 has a central angle .theta..sub.2, and a closed portion 17 defined between adjacent openings has a central angle .theta..sub.3. As shown in FIG. 10, a sector-shaped closed portion 18 is formed between the purge gas supply opening 13b and the exhaust gas supply opening 13a of the rotary valve 12, and also between the purge gas supply opening 13b and the treated gas discharge opening 13c, the sector-shaped closed portion 18 surrounded by the seal member 14 having a central angle .theta..sub.3 and the seal member 14 surrounding the purge gas supply opening 13b having a central angle .theta..sub.1. In this case, the relation between respective angles are defined to be .theta..sub.2.gtoreq..theta..sub.1 and .theta..sub.3.gtoreq..theta..sub.2 ; therefore, at least one of the two sea 14 which partition adjacent openings of the rotary valve 12 from each other is always present in the closed portion 17 of the stationary valve 11. Therefore, at the openings 16 of the stationary valve 11, there is no possibility of the exhaust gas going into mixture with the treated gas, or the exhaust gas going into mixture with the purge gas, or the treated gas going into mixture with the purge gas. Furthermore, clean air is supplied from the purge gas supply opening 13b by a means not shown and, along with the clean air, residual exhaust gas at previous stage of treatment which remains within the heat accumulators 4 is conducted into the combustion chamber 6 and combusted therein. Therefore, when the treated gas is discharged later by being caused to pass through the heat accumulators 4, untreated exhaust gas is prevented from being discharged together with the treated gas.
In above described conventional distributing valve device of the heat-accumulation type combustion system, the relation between the opening 16 and the closed portion 17 of the stationary valve 11 is limited to be .theta..sub.3.gtoreq..theta..sub.2 ; therefore, for example, an area of the opening 16a of the stationary valve 11 cannot be made to be not less than 50% of an area surrounded by the seal member 14. Therefore, considerable pressure loss occurs at the time of gas supply or discharge, and this poses a problem that size enlargement is required with respect to the blower etc..
Another problem is that if an attempt is made to meet the relation of .theta..sub.3 &lt;.theta..sub.2 between the central angle .theta..sub.2 of the opening 16 and the central angle .theta..sub.3 of the closed portion 17 in the stationary valve 11 so as to make the area of the opening of the stationary valve 11 greater than 50% of above-mentioned area, the central angle .theta..sub.2 of the opening 16 of the stationary valve 11 becomes larger than the central angle .theta..sub.3 of closed portion 18 of the rotary valve 12 since the central angel .theta..sub.3 of closed portion 18 of the rotary valve 12 is also .theta..sub.3, as shown in FIG. 11. As a result, the exhaust gas supply opening 13a and the purge gas supply opening 13b are both present within the opening 16, resulting in insufficient purge of residual exhaust gas in the passage 3 within the housing 1. Therefore, the exhaust gas remains in the passage 3 and such exhaust gas residue thereafter becomes mixed with the treated gas as the treated gas is discharged through the passage 3, with the result that smelly substances, such as organic solvent, are diffused into the atmosphere.
Further, since the seal member 14 is conventionally provided on the rotary valve 12, frequent contacts between the seal member 14 and the opening 16 occur. In addition, as shown in FIG. 12, fragments 8 or the like of the heat accumulator 4 within the housing 1 are accumulated on the upper surface of the rotary valve 12. Therefore, the seal member 14 is subject to considerable damage so that exchange of the seal member 14 for new one is urged frequently for maintaining hermetic sealing.